I'm torn between 4 and 5 stars. On the one hand, characters, story and writing are mostly superb. Nothing drags or bores. Interesting and visual scenes throughout. Unpredictable in a good way. Truly engrossing entertainment, and fodder for discussion as high fantasy should be. The best reason why I could consider this a 5 star read is that I plan to read the next book in the series, and I generally avoid serial novels due to often ending up dissatisfied and disgruntled.
So, what not 5 stars? A couple of reasons. First, three characters became annoying caricatures. They lost all depth. (To avoid spoilers, I'll not name the ones I mean.) Greater disclosure into the characters' motivations would have allowed the reader to understand them as something more than the evil witch of the west type villain. In reality, which this novel adheres closer to than other epic fantasies (such as Lord of the Rings), an outright evil person needs motivation unless they are orcs or some other bad to the bone creations. Martin gave perfect motivation to one of the minor evil characters, yet two majors monsters were left flat. Interestingly enough, the other caricature was the 'good' girl role.
My second reason for not giving 5 stars is simply personal preference. The cruelty, rape and violence caused me to cringe a bit too frequently. The story warrants those elements, and I wouldn't deny them, but neither do I find them enjoyable.
Still, this is a laudable work that warrants Mr. Martin being praised in recent reviews. I'm looking forward to reading more.